1. Field of the Invention
The present invention relates a method of arranging in the form of a linear array, a plurality of optical fibers of a kind generally used in optical fiber communication and information processing, a method of fixing the optical fibers in readiness for connection with a corresponding number of similar optical fibers, and a wavelength selecting device utilizing the optical fibers.
2. Description of the Prior Art
Requirements associated with the linear arrangement of optical fibers and the positioning accuracy thereof have now become severe and, at the same time, various attempts have been made to minimize problems brought about by rays of light reflected from end faces of the optical fibers connected with other optical elements. Although the problems brought about by the reflection of light from the end faces of the optical fibers may be substantially eliminated if the end face of each optical fibers is skewed, the optical fibers now in wide use have an end face lying perpendicular to the longitudinal axis thereof.
Hereinafter, one example of the prior art methods of making the conventional linear array of optical fibers referred to above will be discussed.
FIGS. 8(a) and 8(b) are schematic diagrams showing the sequence of manufacture of the conventional optical fiber array, and FIG. 9 is a schematic perspective view of the optical fiber array manufactured by the method shown in FIGS. 8(a) and 8(b). Referring to FIGS. 8 and 9, reference numerals 111 and 112 represent respective blocks; reference numerals 121 and 122 represent guide grooves defined in the associated blocks, respectively; and reference numeral 130 represents a plurality of optical fibers.
The optical fiber array is manufactured in the following manner.
The optical fibers 130 are received in the guide grooves 121 defined in the block 111 so as to be spaced an equal distance from each other as shown in FIG. 8(a). In order to fix the optical fibers 130 in position within the guide grooves 121, the block 112 having the guide grooves 122 defined therein in a pattern matching that of the guide grooves 121 in the block 111 is placed from above onto the block 111 as shown in FIG. 8(b). In this way, the optical fibers 130 are firmly clamped between the blocks 111 and 112.
While the optical fibers 130 are clamped between the blocks 111 and 112, end faces of those optical fibers 130 are ground to complete the optical fiber array as shown in FIG. 9. In this connection, see, for example, a paper by J. Lipson et al. entitled "A Six-channel Wavelength Multiplexer and Demultiplexer for Single Mode Systems" (IEEE Journal of Lightwave Technology, LT-3, No. 5, Page 1159, 1985).
However, the above-discussed prior art method has a problem in that a highly precise machining technique is required in forming the equally spaced guide grooves 121 or 122 in each of the blocks 111 and 112; also, the spacing between each of neighboring ones of guide grooves 121 or 122 is required to be small. Where the plural optical fibers 130 are required to be closely juxtaposed with the minimized spacing between neighboring optical fibers, a more precise positioning accuracy is required. In addition, when stresses are induced between the optical fibers 130 and end faces of the guide grooves 121 and 122 during the positioning of the optical fibers 130, breakage or damage tends to occur at such portions of the optical fibers where the stresses are induced.
Moreover, since the respective end faces of the optical fibers are perpendicular to the associated optical axes thereof, rays of light reflected from those end faces of the optical fibers bring about an adverse influence upon optical elements with which they are to be connected. Yet, even though the optical fibers having inclined end faces are made available, it has been difficult to arrange them at a precisely ground angle.
The prior art wavelength selecting device will now be discussed. The wavelength selecting device is a device for selecting a particular light from the multiplexed light beams used in a wavelength multiplexed optical communication system and, in recent years, various types of wavelength selecting devices have been suggested and examined. Specifically, a wavelength selecting method utilizing a diffraction grating is generally effective to accomplish a highly accurate wavelength selection at a broad band.
One example of the prior art wavelength selecting devices will now be specifically discussed.
FIG. 11 pertains to the structure of the prior art wavelength selecting device, wherein FIGS. 11(a) and 11(b) depict top plan and side views thereof, respectively. In FIG. 11, reference numeral 41 represents an input optical fiber; reference numeral 42 represents a light receiving optical fiber; reference numeral 43 represents a lens; reference numeral 44 represents a diffraction grating; reference numeral 45 represents a rotary mechanism; and reference numeral 46 represents an end face of each of the optical fibers 41 and 42.
The wavelength selecting device operates in the following manner. For the purpose of discussion, the wavelengths are respectively designated by .lambda.a, .lambda.b and .lambda.c in the order from the shortest wavelength.
Wavelength multiplexed beams having the respective wavelengths .lambda.a, .lambda.b and .lambda.c emitted from the input optical fiber 41 are incident on the diffraction grating 44 through the lens 43 and are subsequently diffracted by the diffraction grating 44. Some of the diffracted beams falling in a desired wavelength region are converged by the lens 43 so as to enter the light receiving optical fiber 42, thereby accomplishing a wavelength selection. Specifically, when the diffraction grating 44 while receiving the wavelength multiplexed beams is rotated by the rotary mechanism 45, the beams of respective wavelengths .lambda.a, .lambda.b and .lambda.c can be directed into the light receiving optical fiber 42.
In the construction described above, however, the end face 46 of each of the optical fibers 41 and 42 is ground so as to lie perpendicular to the optical axis of the respective optical fiber 41 or 42 and, therefore, the reflected light tends to be multiply reflected between the two end faces of the input and light receiving optical fibers 41 and 42 and, hence, between a transmitter side and a receiver side, causing a Fabry-Perot resonance. The occurrence of the Fabry-Perot resonance of light tends to adversely affect the quality of transmitted signals particularly in the case of analog transmission.
Also, since the input optical fiber 41 and the light receiving optical fiber 42 are arranged in the same direction as the direction of diffraction of the rays of light from the diffraction grating 44, and if the wavelength multiplexed beams contain a light component of a wavelength whose angle of diffraction matches with the direction of the input optical fiber, the light of such wavelength tends to be coupled to the input optical fiber, bringing about an adverse influence on a transmitter as a back-reflected light. This problem is inherent in, for example, the device disclosed in U.S. Pat. No. 4,763,969.